This invention relates to the railway art and, more particularly, to improved configuration of a railway truck wheel and rails.
In the railway art, the structure of railway trucks with wheelsets, which engage laterally spaced rails has been standardized to facilitate railway transportation within the railway system. The defined standards provide for most efficient profiles of the mutually engaged surfaces of the wheels and rails, while taking into consideration allowable contact and deformation forces acting on the contact surfaces during operation. It is well known that efficient profiles can significantly reduce friction and wear between the rail gage surfaces and the flanges of the wheels running on the rails. Proper rail gage surface and wheel profile can reduce operating costs and extend rail and wheel service life.
Despite recognition of the problem, the industry oftentimes fails to design the most efficient profile configuration. Conventionally, contact stress calculations are conducted using the Hertz Theory, which takes into consideration contact forces between adjoining bodies. Contact stresses are due to weight, driving forces and other types of unusual, mainly dynamic, forces. A simple model calculation based on the Hertz Theory evaluates the effect of the weight only. Moreover, the Hertz Theory can be used only with perfectly elastic bodies under normal loads since Hertz calculated only the surface stresses.
For many years, engineers have been heavily relying on the Hertz Theory for stress calculations. Even more complicated theories consider the driving and other forces as a percentage of weight. Some researches evaluate subsurface stresses considering the contact between two spheres or two cylinders, which creates a circular or rectangular contact area, respectively. With these shapes, the contact area dimensions are determined analytically, by solving simple equations. However, the rail/wheel contact is more complex, it is elliptic due to the interaction between two curved bodies positioned in perpendicular planes. Elliptical contact is the contact between two bodies having different radii of curvature, such as the contact between a rail head and a wheel or wheel rim.
The industry recognizes that many rolling surface defects are due to the failure of the surface to withstand applied loads. The strength depends on the surface hardness, which can be determined by experiments under controlled conditions. Evaluating the loads is more complex and presents a considerable challenge for contact researchers, who attempt to evaluate the stress field inside elastic rolling bodies with an elliptic area of contact.
Additional problems encountered with conventional railway systems include the tendency for the wheel sets to traverse curves in a non-radial orientation and cause the wheel flange to rub against the rail. Such rubbing contact and wheel sliding result in undesirably high wheel and rail wear; when the flange rubs against the side of the rail, the wheel may produce a tendency to climb the rail and cause a derailment. In addition, improper wheel set tracking in curves may result in track misalignment.
A further problem is the possibility of design variations occasioned by imprecise manufacture, assembly, as well as railway deformation. Even further, the designers are often required to theoretically calculate most beneficial contact stresses, without taking into consideration specific dimensions of contact surfaces, precise shapes and site conditions.
The present invention contemplates elimination of drawbacks associated with the prior art and provision of the wheel/rail design, which reduces contact stresses regardless of the particular country's allowed norms and sizes governing rail and wheel specifications.